Articles from Lapidary Digest

FINDING AND FINISHING AMMONITES

Dave Daigle
Edmonton, Alberta, Canada
rokhound@planet.eon.net


Copyright 1997-1998. This document may be copied and used in mineral and gem club newsletters without asking permission, given that the article is reprinted in toto and that cedit is given the author and Lapidary Digest as the source. Others wishing to reprint the article may send a rquest to Lapidary Digest, using the e-mail form on the first page.

...COLLECTING AMMONITES


Somewhere in the Lower Middle Devonian, some group of Nautiloids gave rise to a modest group of coiled Cephalopods, the Ammonites. They really picked up their pace in the Mesozoic Period and became more plentiful and varied, and were dispersed almost worldwide. They differed somewhat from their modern day cousins, mainly by internal structure.

As they died on the ocean floor, they were buried in the sea mud. In North America that mud became, for the purpose of this paper, either shale or Ironstone. Normally the mud would be pressed into flat layers of shale by the pressure of sea and mud above it, but the hard bodies kept their shape and became concretions. Those concretions, or roundish UFO shaped nodules of shale and Ironstone, are found in the Aragonite Zones of the Badlands, in Southern Saskatchewan, Southern and Mid Alberta, and Northern Montana and are the geologic structures where Ammonites are found today. You usually find the concretions in the upper sides of banks on existing rivers, such as the Bow River, or in the Badlands banks, which were rivers at one time. Surface collecting is easiest, although some rockhounds have adapted a type of long tined pitchfork for prodding down into the soft Bentonite beds in hope of striking a concretion.

Once found, the trick is to break open the concretion. If cleaned off carefully, one can usually see small fracture lines or, sometimes, a piece of the Ammonite peeking through a spot at the edge of the nodule. A sharp chisel, a hammer, and a steady hand, and most concretions will break in half where the Ammonite is laying usually exposing a concave side of the concretion with shell attached and the Ammonite itself imbedded in the other half. If you are after the Gem...or shell....then you can break the Ammonite out of the now halved concretion. But, if you want a complete Ammonite, if indeed it is complete, then traditional methods of removing a fossil from matrix are used. Thank goodness for Foredoms and Dremels :)

Trivia time...The Ammonites got their name from the chief God of the Triad of Thebes Amun, who was often depicted as a Ram with curved horns.

The area covered by the Bearspaw Sea, which included Northern Montana, Alberta and Western Saskatchewan is where we find most of the Placenticeras Meeki species. The Meeki is, in my humble opinion, the best gem quality shell. These concretions with, hopefully, Meeki inside of them, can be anywhere from 6" to 3' in diameter! The bigger ones, and most others, are "halved" right there on the spot to see what treasures they hold and to more easily get them back to your transport. Most will fit into a backpack but some we have to "sling" and carry these on our backs also. Heavy?......You Bet !

But alas, sometimes you find the other kind, what we call barren shale, and your efforts of digging them out and breaking them in half are not rewarded.

Hmmm, heavy....reminds me of a time when I was loaded down with a heavy pack full of Ammonite, walking on a game trail at the bottom of a coulee on the way back to my truck. I came around a corner, with my head down..of course, (typical Rockhounding syndrome) and came face to face with a huge Whitetail Buck! Now, it's nice to see nature from a distance, but up close those bucks are huge!!! He startled me and I fell backwards on my pack and watched as the buck took off straight up the side of the coulee like the hounds of hell were chasing it. I recall, as I laid there looking up, that the bank was about 100 feet high and pretty well straight up! Well, after kicking my legs for a while, and laughing at my predicament of looking, for all the world, just like a Turtle flipped on it's back with it's legs wiggling, and rocking my body I finally rolled on my side and managed to get back to my feet. To this day, I still don't know which one of us were scared more, the Buck or me. :)

Do you still want to go hunting for these concretions with that beautiful Ammonite shell inside? A word of warning, you must, at least in Canada, have the appropriate Ammonite permit to collect Ammonites! The fine can be severe for collecting without one. But it doesn't stop with a license; once you have returned home with your collected treasures, you must then fill out a disposition form and take pictures of your finds, which are sent off to the Tyrell Museum, where the experts look things over. If you have not discovered a new species or anything of paleontological value, they send you a reply...and then the Ammonites are yours.




...FROM RAW TO GEM AMMONITE


I will attempt, in my humble way, to describe to you the way in which I work my Ammonite. Please bear with me, as writing is not my forteí.

Once I have gotten my Ammonites home, itís time to clean them and see what Iíve got. This can involve anything from Muriatic acid baths .. .remember AAA, Always Add Acid ... never add water to acid, to a simple cleaning with a brush and water. Some Ammonite has a thin film of white, or unformed, Calcite on top of the gem, this is when Acid is used in dilute amounts to clean it off. If itís too filmy it usually extends down through the shell and makes it rather useless for Gem Quality pieces. Although with acid, the colors are still there.

Next comes the decision to keep it whole..if indeed you found a whole one in one piece, you should keep it as such.....or to "gem it", if itís in many fractured pieces. If itís whole, itís sanded by hand later. Iíve found no better way to do it, although Iíve experimented plenty.

Ammonites, it seems, always start their lives with dark colored, blue or green, shells. Probably to aid them in hiding from their many predators. Their shell is in layers, starting from red, to the oranges and yellows and then to the greens and blues of the last layers. So, if you feel brave, you can continue to sand down through the layers to get at the rare greens and blues. But, like an opal, be careful, after the last blue color...thereís nothing but shale and you will have lost your color!

But alas, I wander off...... Back to it then.:) There is much to do before laying on the sandpaper. Firstly, if not whole, you must cut away the excess shale, this can be a tricky process also. You should try and keep about Ĺ " of shale still attached to the Ammonite Gem. Remember, the Ammonite is a Nautiliod and shaped accordingly, albeit flattened out somewhat from the pressures of time. Therefore there will be gem on "both sides" of the Ammonite, and you have to decide where to cut it. Flat spots are preferred, but they are rare in a Nautiloid shaped body.

Depending upon the color of the shale you probably have to seal the Ammonite. If whole, then you seal the whole Ammonite. But for this paper, letís assume that you have Ammonite pieces. The reason for sealing the Ammonite is to darken the shale down and to seal the gem shell to the shale beneath it. Again, referring to opal, the darker the matrix, such as Black Mintabe Opal, the brighter the color or fire is seen. Same thing with Ammonite gem. The darker the shale below, the brighter the colors of the gem will seem to be.

Sometimes, Ammonites come with the shell sitting loosely on the shale cores. This is where the Opticon Sealer comes in. You need to heat the Ammonite pieces up to about 150 degrees and the apply the sealer to the gem with a brush. I use sheets of Ĺ inch steel and lay them across the burner elements of a kitchen range. But if youíre doing a single piece, or just a few, a slow oven will do just nicely. The warm stone will actually draw the sealer down through the gem and into the shale beneath it, thus effectively sealing the
gem to the shale and making the shale darker. Take the pieces off the heat and let them sit for a few days. The sealer never quite seems to harden, but almost.

Now, the pieces have to be cut into your fairly flat pieces or freeforms. Not too small yet as you have to use the Lap wheels next. I guess this part just takes practice, but you can actually find some fairly flat pieces on the Ammonite .... you just have to picture flat enough places and sizes to eventually make gems from. Sometimes your pieces are small. But they are flat! :)

The Gem Quality of the pieces are important and could alter your decision for gem or freeform pieces. "A" grade or better have a finely fractured texture with either a multitude of colors or a single brilliant color. The grades differ to c,b, a,aa,and triple a grades. Now that we have formed the AFAC we hope that the grades can be regulated. But for now beware, some peoples ideas of A grade are not always the same as someone elses. Some gem has wide fracture lines and poorer colors and are therefore of lesser quality. After you done it for a while, you can tell this when you first crack open the concretion.

Next comes the flat laps. I usually start with about a 400 grit ...carefully ...the gem is not that hard. Think of it as a regular shell and youíll be fine. All you want to do in this stage is to "flatten" the piece you are working on. Some of it, of course, can never be flattened and I believe these pieces would be great for intarsia work, but since I havenít got that figured out yet, for freeform pieces. Once you have your piece fairly flat, look at the center of the piece, youíll probably find...if you stopped soon enough .. that itís the green or blue color. If you didnít stop soon enough, then youíll find shale,...Damn! And you start over with a flatter piece. :) Seriously though, keep an eye on it and youíll be fine. This is the stage where you must decide, freeform or gem quality. If you are doing gems instead of freeform, you cut out your gems before you start your 600 stage. The most popular way to cut the gems .... which also gives you the least waste...is the rock bandsaw. But, the traditional saw is fine, just plan your gems out carefully as to waste as little of it as possible.....itís expensive stuff!! An oval of 10x14 can be $80.00 or more if itís of "AA" or better!

I dop my gems with a two part 5 min epoxy on to welding rod pieces. Just warm up the metal rods with a torch slightly and stick it to the already placed epoxy on the back of the gem (the shale). I round them into calibrated shapes with a 400 or 600 grit expandable wheel with sc grit.

Finally, the gem must be capped. Some Lappers use glass, some use a product such as Envirotex .. a two part sealer/glue that hardens rock solid. These methods are ok, but for rings and high abuse jewellery you still canít beat Spinel or Quartz Caps. I use tempered glass or I make my own caps from Quartz, for Brooches and most of my freeforms.

I hope I have been able to shed some light on the long kept secrets of Ammonite Gems. But if we are going to sell rough, people need to know how to work it properly. Itís too precious and beautiful a gem for people to have to learn the hard way, as I did.